The present invention relates to a reactor for biological treatment of water, including drinking water, municipal and industrial wastewater, and hazardous waste.
Water quality is of increasing importance, as many of the impurities in water have been identified to have deleterious effect in the environment or for plant or animal life. Both water from streams, rivers, etc. and wastewater require treatment to reduce the pollutants in the water to acceptable levels.
Wastewater emanates from four primary sources: municipal sewage, industrial wastewaters, agricultural runoff, and storm water and urban runoff. For purposes of the present invention, the term xe2x80x9cwastewaterxe2x80x9d will include water from any or all of these sources.
Wastewater can be purified by a variety of methods, including mechanical purification by sedimentation or filtration (usually surface waters for drinking water treatment), and chemical purification by, for example, the addition of ozone or chlorine (not practical as standalone for wastewater treatment). Biological wastewater treatment is by far the most widely used technology for treating municipal and industrial wastewater in the U.S., and it is gaining popularity for the treatment of drinking water.
Biological treatment of water and wastewater requires an intimate contact between microbes and the water being treated and establishment of an environment conducive to the growth of the microorganisms utilizing the contaminants in the water. For efficient utilization of space and effective treatment, these processes typically concentrate the microbes either by using a settling tank or attaching the microbes to fixed surfaces from which biomass solids may slough. The settling tank is used both to concentrate the biomass for recycling back to the aeration tank and for separation (clarification) of the biomass from the effluent prior to discharge.
More recently, membrane technology has been used for biomass concentration and separation from the treated water. These devices, typically referred to as membrane bioreactors (MBRs), achieve biomass separation using either polymeric or ceramic membranes. The membranes can be either located within the bioreactor or placed external to the bioreactor. When placed within the bioreactor, these units are operated either by applying a partial vacuum on the permeate side of the membrane or by applying pressure to the mixed liquor (biomass) side of the reactor. When the membrane is placed external to the aeration chamber, mixed liquor is pumped at a high flow rate or pressure across this external membrane to achieve separation.
Problems associated with conventional treatment systems are the loss of solids in the treated effluent and the frequent failure of settling tanks to deliver clarified effluents that meet discharge limitations. Conventional membrane bioreactors rely on pressure or vacuum to achieve liquid flux and solids separation. Although MBRs deliver excellent effluent quality, MBRs suffer from high capital and operating costs.
It is an object of the present invention to overcome deficiencies in the prior art.
It is another object of the present invention to provide a gravity-flow biomass concentrator reactor.
It is a further object of the present invention to provide a gravity-flow biomass concentrator reactor which effectively retains and concentrates suspended solids from the water treated therewith.
It is still another object of the present invention to provide a gravity-flow biomass concentrator reactor that can be used under either aerobic or anaerobic conditions.
According to the present invention, a gravity-flow Biomass Concentrator Reactor (BCR) is provided which comprises a porous barrier having pore sizes averaging from about 1 to about 50 microns through which treated water permeates under the pressure of gravity. Solids suspended in water treated with the BCR are effectively retained and concentrated on one side of the barrier.
The gravity-flow Biomass Concentrator Reactor comprises a vessel for holding at least one porous barrier, an inlet for water to be treated such that water flows by gravity through the porous barrier, and an outlet for treated water.
The porous material used in the BCR can be of modular design with the size and number of modules dependent on the flow to be treated, or it can be one large continuous monolith. The porous material used in the BCR can be any suitable porous material. To date, only porous polyethylene walls have been used, although other materials that serve the same function can be substituted for the porous polyethylene. Examples of such other materials include polymeric or ceramic membranes, synthetic or natural woven cloth materials, etc.
The BCR is operated by directing contaminated water into the reactor and allowing microorganisms to biodegrade the contaminants in the water. The treated water permeates through the porous walls of the reactor under the force of gravity while the biomass is retained within the reaction space. This is conceptually similar to currently utilized MBRs except that selection of the pore size of the porous walls allows for gravity flow of the treated water through the porous wall. Selection of the proper pore size can permit continued operation of the system without the need for maintenance above and beyond what is practiced currently with MBRs.
The porous wall provides the separation between the biologically active treatment side and the product water collection parts of the reactor. When operated under aerobic conditions, the biologically active side is mixed by simple diffused air aeration with or without the assistance of water recycling. When the BCR is operated under anaerobic conditions, water recycling or mechanical mixing provide the intimate contact needed between the microorganisms and contaminants. Recycling can be achieved by pumping water at a high flow rate from the tail end of the reactor to the head end, while mechanical mixing could be provided via many of the available mixing devices currently used in anaerobic digestion. No other differences exist when operating under anaerobic conditions.